Thin film lubricant for advanced tribological performance of storage medium

ABSTRACT

A lubricant for improving the durability and reliability of recording media used in hard drives is disclosed. The lubricant comprises a perfluoropolyether main chain with a first end attached to a hexa(trifluoromethylphenoxy) cyclotriphosphazene, a second end attached to a bonding enhancer for enhancing bonding between the lubricant and a carbon-containing layer. The bonding enhancer of the lubricant can contain multiple hydroxyl, amide groups, 2,3-dihydroxy-1-propoxyl, acetamide, methacrylate, methyl methacrylate and glycidyl ether. Some bonding enhancers such as methacrylate, methyl methacrylate or glycidyl ether, can be further activated with ultraviolet light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of disc drivestorage, and more particularly to lubricants used in disc drives toimprove tribological properties.

2. Description of the Related Art

Computer disc drives commonly use components made out of thin films tostore information. Both the read-write element and the magnetic storagemedia of disc drives are typically made from thin films.

FIG. 1 is an illustration showing the layers of a conventional magneticmedia structure including a substrate 105, a seed layer 109, a magneticlayer 113, a diamond like carbon (DLC) protective layer 117, and a lubelayer 121. The initial layer of the media structure is the substrate105, which is typically made of nickel-phosphorous plated aluminum orglass that has been textured. The seed layer 109, typically made ofchromium, is a thin film that is deposited onto the substrate 105creating an interface of intermixed substrate 105 layer molecules andseed layer 109 molecules between the two. The magnetic layer 113,typically made of a magnetic alloy containing cobalt (Co), platinum (Pt)and chromium (Cr), is a thin film deposited on top of the seed layer 109creating a second interface of intermixed seed layer 109 molecules andmagnetic layer 113 molecules between the two. The DLC protective layer117, typically made of carbon and hydrogen, is a thin film that isdeposited on top of the magnetic layer 113 creating a third interface ofintermixed magnetic layer 113 molecules and DLC protective layer 117molecules between the two. Finally the lube layer 121, which is alubricant typically made of a polymer containing carbon (C) and fluorine(F) and oxygen (O), is deposited on top of the DLC protective layer 117creating a fourth interface of intermixed DLC protective layer 117molecules and lube layer 121 molecules.

The durability and reliability of recording media is achieved primarilyby the application of the DLC protective layer 117 and the lube layer121. The DLC protective layer 117 is typically an amorphous film calleddiamond like carbon (DLC), which contains carbon and hydrogen andexhibits properties between those of graphite and diamond. Thin layersof DLC are deposited on disks using conventional thin film depositiontechniques such as ion beam deposition (IBD), plasma enhanced chemicalvapor deposition (PECVD), magnetron sputtering, radio frequencysputtering or chemical vapor deposition (CVD). During the depositionprocess, adjusting sputtering gas mixtures of argon and hydrogen variesthe concentrations of hydrogen found in the DLC. Since typicalthicknesses of DLC protective layer 117, are less than 100 Angstroms,lube layer 121 is deposited on top of the DLC protective layer 117, foradded protection, lubrication and enhanced disk drive reliability. Lubelayer 121 further reduces wear of the disc due to contact with themagnetic head assembly.

Although conventional lubricants have been used to lubricate disks inhard drive applications, there are problems with using conventionallubricants in media for modern disc drives applications. For example,modern media use much thinner layers and much thinner lubricants thanolder media from just a few years ago and as the thickness of theprotective layers 117 and lube layers 121 are reduced, reliabilityproblems arise. A more integrated protection structure is needed thatwill produce a more durable protective film without effectingthicknesses. Reliability of hard disks is heavily depended upon thedurability of the thin film media.

Lubrication additives, such asBis(4-fluorophenoxy)-tetrakis(3-trifluoromethyl phenoxy)cyclotriphosphazene (X1P), have been used to improve tribologicalperformance and corrosion resistance of thin film media. Although thesenew lubricant that contain additives are an improvement over oldlubricants, there are still many tribological problems associated withthem including lubricant pick-up, head smear, high stiction, and otherproblems resulting from weak bonding of the lubricant andcarbon-containing overcoat. Additionally, since lubricants containingredients, that deteriorate tribological performance, if allowed tobuild up on the medium, the chemical compositions of both the lube bathand lubricant film on the medium must be closely monitored to preventunexpected fall-off of tribological performance.

Therefore what is needed is a lubricant that overcomes these problems,provides better tribological performance and provides desirableproperties. Desirable properties include a resulting lubricant that doesnot have problems such as phase separation, lubricant pick-up, headsmear, high stiction, etc.

SUMMARY OF THE INVENTION

These limitations are overcome by using a lubricant having aperfluoropolyether main chain with a first end attached to ahexa(trifluoromethylphenoxy) cyclotriphosphazene, a second end attachedto a bonding enhancer for enhancing bonding between the lubricant and aprotective carbon-containing overcoat layer. The bonding enhancer of thelubricant can contain multiple hydroxyl, amide groups,2,3-dihydroxy-1-propoxyl, acetamide, methacrylate, methyl methacrylateand glycidyl ether.

In one embodiment of the invention the bonding enhancer of the lubricantis activated when exposed to ultraviolet light. For example, if thebonding enhancer is methacrylate, methyl methacrylate or glycidyl ether,then ultraviolet light can be used to activate the bonding enhancer.

In another embodiment, the lubricant contains a compound having theformula:

Another embodiment of the invention comprises a magnetic recording mediacontaining a lubricant having a perfluoropolyether main chain with afirst end attached to a hexa(trifluoromethylphenoxy)cyclotriphosphazene, a second end attached to a bonding enhancer forenhancing bonding between the lubricant and a carbon-containing layer.The magnetic recording media can further include a substrate, a magneticlayer for recording information, a protective carbon-containing overcoatfor protecting the magnetic layer, and a lubricant deposited over theprotective overcoat.

Another embodiment of the invention comprises a hard drive used forstoring information containing a magnetic recording media comprising amagnetic layer, a protective carbon-containing overcoat, and a lubricanthaving a perfluoropolyether main chain with a first end attached to ahexa(trifluoromethylphenoxy) cyclotriphosphazene, a second end attachedto a bonding enhancer for enhancing bonding between the lubricant and acarbon-containing layer. The hard drive used for storing informationfurther includes a transducer for recording and retrieving informationfrom said magnetic recording media; and a motor for rotating themagnetic recording media.

These and various other features as well as advantages whichcharacterize the present invention will be apparent upon reading of thefollowing detailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram showing a prior art conventional magneticmedia structure with a lubricant layer;

FIG. 2 shows a chemical structure of a lubricant made in accordance withone embodiment of the invention;

FIG. 3 shows a schematic procedure used to synthesize an Xt-PFPElubricant, which contains a 2,3-dihydroxy-1-propoxyl, in accordance withone embodiment of the invention;

FIG. 4A is a graph showing Gel Permeation Chromatography spectra for aconventional lubricant in a lube-bath as a function of time at variousstages of usage;

FIG. 4B is a graph showing Gel Permeation Chromatography spectra forXt-PFPE lubricant in a lube-bath as a function of time at various stagesof usage;

FIG. 5 is a block diagram showing a magnetic media structure havinglubricant layer made with the chemical structure of FIG. 2 above;

FIG. 6 shows the Lube Bonding Ratio (%) for a conventional lubricant andXt-PFPE both with and without ultraviolet light exposure; and

FIG. 7A and FIG. 7B are graphs showing Contact Stop Start (CSS) testingdata for magnetic media lubricated with Xt-PFPE lubricant, in accordancewith one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a system and method for protecting magneticmedia. The invention is directed to a lubricant and a magnetic mediastructure having the lubricant. The magnetic media structure includesthe new lubricant that has been deposited over a magnetic mediastructure both with and without ultraviolet (UV) light for enhancement.

FIG. 2 shows a chemical structure of a lubricant 200 made in accordancewith one embodiment of the invention. The chemical structure oflubricant 200 includes a perfluoropolyether (PFPE) main-chain 210 withone end attached to a hexa(trifluoromethylphenoxy) cyclotriphosphazene215, and the other end attached to a bonding enhancing group B 220 thatcan enhance bonding on a carbon-containing overcoat. Thehexa(trifluoromethylphefloxy) cyclotriphosphazene 215 provides themedium good durability. The bonding enhancing group B 220 can includechemical groups with multiple hydroxyl, amide groups or chemical groupssuch as 2,3-dihydroxy-1-propoxyl, acetamide, methacrylate, methylmethacrylate and glycidyl ether. The bonding enhancing group B 220compounds have the property of being strongly bonded to acarbon-containing overcoat. Specifically, the methacrylate, methylmethacrylate and glycidyl ether compounds bond strongly to acarbon-containing overcoat when activated by being exposed toultraviolet (UV) light whereas the 2,3 dihydroxy-1-propoxyl compoundsbond strongly to a carbon-containing overcoat without being exposed toUV light. Additionally, attaching bonding enhancing chemical group B 220can make purification of the resulting lubricants easier by using aliquid chromatography process.

FIG. 3 shows a schematic procedure used to synthesize an Xt-PFPElubricant, which contains a 2,3-dihydroxy-1-propoxyl, in accordance withone embodiment of the invention. Xt-PFPE lubricant is synthesized byfirst dissolving Zdol and trifluoro-m-cresol in stoichiometric ratio ina mix solution of Vertrel Xf and tetrahydrofuran. Sodium hydride powderis added slowly. Phosphonitrilic chloride trimmer in tetrahydrofuran isadded dropwise and the system is refluxed for more than three days toallow the reaction to be finished. Next, excess amounts ofepichlorohydrin are added slowly with a syringe, followed by addition ofexcess amounts of KOH aqueous solution. Next, the solution is pouredinto a 1N KOH aqueous solution, which opens the epoxy ring to form a2,3-dihydroxy-1-propoxyl group. After washing the product with brinesolution and de-ionized water multiple times, and distillation to getrid of solvent, a crude oil is obtained. Next, further purification ofthe crude oil is performed using liquid chromatography. Xt-PFPE can beeasily separated from reaction byproducts when using Vertrel Xf as theeluant. Finally, the lubricant is fractionated to obtain a fraction withdesirable molecular weight and distribution using Supercritical FluidExtraction.

FIG. 4A is a graph showing Gel Permeation Chromatography (GPC) spectrafor a conventional lubricant in a lube-bath as a function of time atvarious stages of usage. GPC Graph 410 shows GPC data for theconventional lubricant at the early stages of usage whereas GPC Graph420 shows GPC data for the same conventional lubricant after a period ofusage. The difference between GPC Graph 410 and GPC Graph 420 shows thatthe chemical composition of a conventional lubricant changes over time.For example, the peak seen in GPC Graph 410 around 19 minutes issignificantly reduced if not eliminated in GPC Graph 420. Similarly thepeak located around 23-24 minutes is significantly bigger for GPC Graph420 then it is for GPC Graph 410. Additionally, GPC Graph 410 and GPCGraph 420 show that the conventional lubricant contains multiplecomponents whose composition changes over time. This change in theconventional composition is attributed to irregular tribologicalperformance of the lubricant.

FIG. 4B is a graph showing Gel Permeation Chromatography spectra forXt-PFPE lubricant in a lube-bath as a function of time at various stagesof usage. GPC Graph 430 shows GPC data for Xt-PFPE lubricant in alube-bath at the early stages of usage whereas GPC Graph 440 shows GPCdata for Zdol used in the reaction. GPC Graph 430 shows that Xt-PFPE hasa much simpler chemical composition than does the conventionallubricant. The simpler chemical composition of the Xt-PFPE lubricantprovides a lube-bath with a constant chemical composition, which doesnot change with time as much as the composition of the conventionallubricant.

FIG. 5 is a block diagram showing an Xt-PFPE lubrication layer 530 in amagnetic media 500 in accordance with one embodiment of the invention.Magnetic media 500 includes a substrate 510, a seed layer 515, amagnetic layer 520, a protective overcoat layer 525, and an Xt-PFPElubrication layer 530. The substrate 510 is typically made ofnickel-phosphorous plated aluminum or glass that has been textured. Theseed layer 515, typically made of chromium, is a thin film that isdeposited onto the substrate 510 creating an interface of intermixedsubstrate 510 layer molecules and seed layer 515 molecules between thetwo. The magnetic layer 520 is typically made of one or more magneticalloys comprising cobalt (Co), platinum (Pt) and chromium (Cr).Additionally, magnetic layer 520 can be a thin film structure made ofmagnetic alloy and spacer layers. Magnetic Layer 520, is a thin film orstack of thin films deposited on top of the seed layer 515.

Protective overcoat layer 525 is typically made of a carbon-containingmaterial such as diamond-like-carbon (DLC), nitrogenated carbon, ornitrogenated DLC. The protective overcoat 525 is typically depositedover magnetic stack 520 using conventional thin film depositiontechniques including ion beam deposition (IBD), plasma enhanced chemicalvapor deposition (PECVD), magnetron sputtering, radio frequencysputtering, or chemical vapor deposition (CVD). In one embodiment, theDLC protective layer 525 is prepared by ion beam deposition using a workgas is C₂H₂. The energy per C atom is 90 eV.

Xt-PFPE lubrication layer 530 includes hybrid lubricant films containinga perfluoropolyether (PFPE) main-chain 210 with one end attaching to ahexa(trifluoromethylphenoxy) cyclotriphosphazene 215, and the other endto a bonding enhancing group B 220 that can enhance bonding between theXt-PFPE lubricant and the carbon-containing overcoat, as described withreference to FIG. 2. Conventional lubrication processes such as dippingcan be used to apply the lubricant. Lubricant layer 530 can be appliedboth with and without exposure to UV light depending on the enhancinggroup B 220. Since lubricant layer 530 bonds to the carbon-containingovercoat better than conventional lubricants, lubricant pickup isreduced; head smear is reduced; fly stiction is improved; and CSSdurability of thin film storage media is improved. Evidence that thestronger bonding between the Xt-PFPE lubricant and the carbon-containingovercoat reduces lubricant pick-up and head smear is presented belowwith reference to FIG. 6 and FIG. 7.

Magnetic media 200 with Xt-PFPE lubrication layer 530 can also be usedin a disc drive to give improved performance. A disc drive using amagnetic-media 500 with Xt-PFPE lubrication layer 530 also includes amotor for spinning the magnetic media at many thousand revolutions perminute about its center of rotation, a transducer for magneticallyreading and writing information on the magnetic media while the magneticmedia is rotated about its center axis. Those skilled in the art willrecognize that other components needed to construct a disk drive such asthe housing and Head-Stack-Assembly are also included and all aremaintained within a housing. The Xt-PFPE lubrication layer 530 permitsthe transducer, which is mounted on a glide assembly, to glide over therotating disk reliably for long periods of time.

FIG. 6 is a bar graph showing and comparing the lube bonding ratio (%)of a conventional lubricant and Xt-PFPE lubricant, both with and withoutultraviolet light (UV) exposure. The bonded lubricant thickness data ofFIG. 6 is measured after excessive lubricant, often called “freelubricant,” is washed off the disks by using vapor condensation oflubricant solvents such as Vertrel Xf. The percentage of the bondedlubricant thickness in the total lubricant thickness is called lubricantbonding ratio. The graph shows that the lube bonding ratio for aconventional lubricant is about 30% without exposure to UV light andabout 52% with exposure to UV light. The graph also shows that the lubebonding ratio for Xt-PFPE lubricant is about 50% without exposure to UVlight and about 79% with exposure to UV light. A comparison of thegraphs shows 1) the lube bonding ratio for Xt-PFPE is higher than for aconventional lubricant when neither are treated with UV light, 2) thelube bonding ratio for Xt-PFPE is higher than for a conventionallubricant when both are treated with UV light, 3) the lube bonding ratiofor Xt-PFPE is higher than for a conventional lubricant when Xt-PFPE istreated with UV light but the conventional lubricant is not treated withUV light, and 4) the lube bonding ratio for Xt-PFPE is similar to thatof a conventional lubricant when Xt-PFPE is not treated with UV lightbut the conventional lubricant is treated with UV light. The FIG. 6graphical data also suggests that even if a conventional lubricant issubjected to UV light its lube bonding ratio can only be made as high asthe Xt-PFPE ratio without exposure to UV light.

Therefore, several advantages of using an Xt-PFPE lubricant are that ahigher lube bonding ratio can be obtained and if a lower lube bondingratio is desired then the step of exposing the lubricant to UV light canbe eliminated because Xt-PFPE has a higher lube bonding ratio than aconventional lubricant without UV exposure.

The UV exposure process is performed using mercury-discharging lamps andinvolves using a process chamber that is purged with Nitrogen during theprocess to prevent Ozone formation. The process time is varied tocontrol the desired outcome and typically ranges from 10 to 120 seconds.

FIG. 7A and FIG. 7B are graphs showing Contact Stop Start (CSS) testingdata for two magnetic media samples lubricated with Xt-PFPE lubricant,in accordance with one embodiment of the invention. FIG. 7A shows thatXt-PFPE lubricated media has very low stiction for cycles less than15000 and only a slightly higher stiction for cycles above 15000.Similarly, FIG. 7B shows very low stiction for almost all cycles exceptfor the occasional small increase in stiction at a few isolated cycles.Overall, FIG. 7A and FIG. 7B show that the Xt-PFPE lubricated mediademonstrates promising CSS durability as well as low stiction inaggressive environmental conditions on thin carbon-containing overcoat.

It will also be recognized by those skilled in the art that, while theinvention has been described above in terms of preferred embodiments, itis not limited thereto. Various features and aspects of theabove-described invention may be used individually or jointly. Further,although the invention has been described in the context of itsimplementation in a particular environment and for particularapplications, those skilled in the art will recognize that itsusefulness is not limited thereto and that the present invention can beutilized in any number of environments and implementations.

1. A lubricant, comprising: a perfluoropolyether main chain having afirst end and a second end; a hexa(trifluoromethylphenoxy)cyclotriphosphazene attached to said first end of perfluoropolyethermain chain; and a bonding enhancer attached to said second end ofperfluoropolyether main chain for enhancing bonding on acarbon-containing overcoat.
 2. The lubricant of claim 1 wherein saidbonding enhancer comprises a 2,3-dihydroxy-1-propoxyl compound.
 3. Thelubricant of claim 1 wherein said bonding enhancer is selected from agroup consisting of methacrylate, methyl methacrylate and glycidylether.
 4. The lubricant of claim 1 wherein said bonding enhancer isselected from the group consisting of multiple hydroxyl, amide groups,2,3-dihydroxy-1-propoxyl, acetamide, methacrylate, methyl methacrylateand glycidyl ether.
 5. The lubricant of claim 1 wherein said bondingenhancer is activated when exposed to ultraviolet light.
 6. Thelubricant of claim 3 wherein said bonding enhancer is activated whenexposed to ultraviolet light.
 7. The lubricant according to claim 1wherein said lubricant comprises a compound having the formula


8. A lubricant, comprising: a perfluoropolyether main chain having afirst end and a second end; a hexa(trifluoromethylphenoxy)cyclotriphosphazene attached to said first end of perfluoropolyethermain chain; a bonding enhancer attached to said second end ofperfluoropolyether main chain for enhancing bonding on acarbon-containing overcoat; and said bonding enhancer selected from thegroup consisting of methacrylate, methyl methacrylate and glycidylether.
 9. The lubricant of claim 8 wherein said bonding enhancer isactivated by being exposed to ultraviolet light.
 10. A lubricant,comprising: a perfluoropolyether main chain having a first end and asecond end; a hexa(trifluoromethylphenoxy) cyclotriphosphazene attachedto said first end of perfluoropolyether main chain; a bonding enhancerattached to said second end of perfluoropolyether main chain forenhancing bonding on a carbon-containing overcoat; and said bondingenhancer is a 2,3-dihydroxy-1-propoxyl compound.
 11. A magneticrecording media, comprising: a substrate; a magnetic layer for recordinginformation; a protective overcoat for protecting said magnetic layers,said overcoat comprising carbon; and a lubricant deposited over saidprotective overcoat, said lubricant comprising: a perfluoropolyethermain chain having a first end and a second end; ahexa(trifluoromethylphenoxy) cyclotriphosphazene attached to said firstend of perfluoropolyether main chain; and a bonding enhancer attached tosaid second end of perfluoropolyether main chain for enhancing bondingon a carbon-containing overcoat.
 12. A hard drive used for storinginformation, comprising: a magnetic recording media, comprising: amagnetic layer for recording information; a protective overcoat forprotecting said magnetic layers, said overcoat comprising carbon; and alubricant deposited over said protective overcoat, said lubricantcomprising: a perfluoropolyether main chain having a first end and asecond end; a hexa(trifluoromethylphenoxy) cyclotriphosphazene attachedto said first end of perfluoropolyether main chain; and a bondingenhancer attached to said second end of perfluoropolyether main chainfor enhancing bonding on a carbon-containing overcoat; a transducer forrecording and retrieving information from said magnetic recording media;and a motor for rotating said magnetic recording media.
 13. A magneticmedia comprising: means for magnetically storing and retrievinginformation on a rotating surface; and means for lubricating saidrotating surface.